High-temperature oxidation of ion-plated TiN and TiAlN films
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The high-temperature oxidation of TiN, Tio.9Alo.1N, and Tio.6Alo.4N films which were deposited onto stainless steel substrates using an arc ion-plating apparatus was studied at temperatures ranging from 923 to 1173 K for 0.6 to 60 ks in air. The oxidation rate obtained from mass gain as a function of time was found to fit well to a parabolic time dependence. From their temperature dependence, the apparent activation energies of oxidation were determined. With increasing Al contents, the oxidation rate decreased, and the activation energies of oxidation reaction increased. Formed oxide layers were analyzed by XRD, SEM, and EPMA. With increased Al content in TiAIN films, the rate-determining step changes from oxygen ion diffusion in formed rutile to oxygen or aluminum ion diffusion in the formed AI2O3 layer.
I. INTRODUCTION The metallic nitride films such as titanium nitride have high hardness, strengths, and wear resistance. Therefore, these films have been applied extensively as the coatings on cutting tools, die molds, and so on. The performance of coated parts depends on not only mechanical properties such as hardness and friction coefficient, but also corrosion resistance of coated film. TiN coatings deposited by physical vapor deposition (PVD) have been successfully applied in industrial usage for wear resistance, but they suffer from a limited oxidation resistance. For nitride coatings, there are many reports with respect to mechanical properties such as hardness, adhesion, and wear resistance.1"4 However, there are few reports on the high-temperature oxidation of nitride films. TiN starts to oxidize already at temperatures as low as 823 K.5 Miinster and Schlamp5 concluded that the kinetics of the oxidation reaction for TiN films deposited by chemical vapor deposition (CVD) follow a linear-parabolic law, and the initial interface reaction control yields rapidly to a diffusioncontrolled mechanism. Tampieri et al.6 reported that the oxidation of hot-pressed TiN ceramics indicates diffusion-controlled kinetics where the diffusion of oxygen or the desorption of nitrogen through the oxide scale would be the rate-governing step. In order to improve the oxidation resistance of TiN films, Miinz7 prepared TiAIN films by using a sputter arc ion-plating. He found the incorporation of Al ions into TiN film gives higher oxidation resistance as well as increased cutting performance of drills. However, Miinz did not investigate the oxidation behavior of TiAIN films from the kinetic point of view. Welsch and Kahveci8 have investigated the oxidation kinetics of titanium aluminum J. Mater. Res., Vol. 8, No. 5, May 1993
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alloy at temperatures between 873 and 1373 K. They reported that the activation energies of oxidation derived from the temperature dependence in the parabolic rate constant increased with increasing Al contents in the alloy. In this paper, the high-temperature oxidation of TiN and Ti^Al^N (JC = 0.1 and 0.4) films that were deposited onto stainless steel su
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